The ability of pathogens to acquire iron from the iron-deficient mammalian environment is important determinant in pathogenesis. Two iron transport systems (Ybt and Yfe) function in Yersinia pestis. The Ybt system is similar to a complex siderophore system of other bacteria. Yfe transport encodes homologues of transporters which include an ATP binding component. Mutations in either of these systems affect virulence, presumably by the inability of the bacteria to grow under iron limitation. The aims of this project are a biochemical and genetic characterization of the transport components of these iron transport systems, and determination of their physiological role in virulence. Regulatory elements and their targets will be identified using reporter-gene fusions, transcript mapping and protein-DNA binding studies. Iron utilization, transport, and binding studies will determine the roles of the of Ytb and Yfe systems in bacterial metabolism and in virulence regulation. Mutants in each system will be constructed and these will be examined for their survival in fleas, macrophages and animals. Expression of the ybt and yfe genes will be analyzed in macrophages and in animals, in order to identify the environments where they are activated. Finally, antibodies will be prepared for some of the surface-exposed components, in order to assess their protective efficacy. Theses studies should lead to improvements in our understanding of the composition and function of the iron transport systems in the context of the disease process, and may provide additional candidates for protective vaccination targets for drug design.